The invention relates to a device for detecting transmission losses of optical light guide means of an endoscope by means of measurements.
An examination of endoscopes and associated light guide cables has frequently shown that the light guide means suffer high transmission losses. Due to mechanical stress, such as bending and winding-up of the light guide cable, tensile stresses when a light guide cable is strongly pulled, bending of the endoscope shaft, and thermal stress during hot-steam sterilization, individual fibers of the light guide means may break. Frequently, there are deposits on the optical inlet and outlet surfaces of the optical inlet and outlet portions. These deficiencies do normally not lead to an immediate failure of the overall illumination means but to a progressive deterioration of the transmission. Owing to the gradual transition to higher transmission losses the deterioration of the illumination intensity is frequently detected too late. If the surgeon notes during an operation that the endoscope used cannot adequately illuminate the operating area, he has to stop the operation in most cases since there is no further sterilized endoscope available to him.
It would therefore be necessary to check the endoscopic instruments prior to their use.
Instruments for determining various photometric measured variables are known. These instruments use an optical sensor for detecting the light emerging from the light source via the light guide means.
DE 35 15 612 A discloses a light source instrument for an endoscope with a checking means for the light source. An examination the light guide cables or an endoscope is not intended.
In DE 43 25 671 A a method and a device for measuring the damping effect in light wave guides using a pulsed light transmitter is disclosed. The transmitter signal is subjected to a pulse frequency modulation with the aid of which variations in the output power are eliminated. This measuring method is very exact but too complex for quickly checking light guide means in operating theaters.
From EP 0 416 408 A a checking means is known where the light source of the endoscopic means comprises a beam splitter in the beam path. A portion of the light beam is directed to a first sensor, while the other portion is directed via a light guide cable to be checked to a second sensor. By comparing the measured values of the first and the second sensor the transmittance is determined. It is of disadvantage that two light sensors are required which may have different sensitivities and thus have to be calibrated. Splitting of the light beam with the aid of a beam splitter also requires careful calibration. The checking means does not possess its own light source and therefore depends on the light source of the endoscopic means such that additional brightness limit values must be fixed to assess the light intensity of the light source. It is disadvantageous that the checking means is integrated into an existing endoscopic equipment and cannot be generally used for checking light guide means of an endoscope. In particular, the known means allows only light guide cables or the lamp of the light source of a specific means to be checked, but not the endoscope proper.